Earth drilling apparatus

ABSTRACT

A drilling apparatus for pressure drilling through the earth, comprising a drill string, a casing tube assembly, a rotary drilling machine with mechanized drill string handling and a liquid handling system. The liquid handling system comprises means for controlling the casing tube pressure and the liquid level within the drill string during withdrawal and disconnection of the drill string. At disconnecting a drill string section, a pressure air impulse is introduced into the flushing channel thereof so as to lower the liquid level and thereby avoid liquid over-flow at the top of the casing tube. A back-flow restricting valve prevents rapid rising of the liquid level within the drill string. A preventer unit having a pressure balanced packing sleeve seals off the upper end of the casing tube; the contact pressure of said packing sleeve is automatically and continuously adapted to the actual casing tube pressure by means of a pressure responsive control valve which is arranged to release the packing sleeve from pressure in response to decreasing casing tube pressure.

United States Patent 1191 Persson 1 EARTH DRILLING APPARATUS [75]Inventor: Jan Edvard Persson, Nacka, Sweden [73] Assignee: Atlas CopcoAktiebolag, Nacka,

Sweden 22 Filed: Aug. 2, 1973 21 Appl. No.: 384,953

[30] Foreign Application Priority Data Aug. 7, 1972 Sweden 10239/72 [56]References Cited UNITED STATES PATENTS 3/1940 Seamark 277/31 3/1952Sausa 251/5 X 3,145,995 8/1964 Adamson et a1. 166/53 X 3,492,007 1/1970Jones 166/84 X 3,614,111 10/1971 Regan 251/1 X 1 June 17, 1975 PrimaryExaminer-Martin P. Schwadron Assistant Examiner-Richard Gerard Attorney,Agent, or Firm-Flynn & Frishauf [57] ABSTRACT A drilling apparatus forpressure drilling through the earth, comprising a drill string, a casingtube assembly, a rotary drilling machine with mechanized drill stringhandling and a liquid handling system. The liquid han- 'dling systemcomprises means for controlling the casing tube pressure and the liquidlevel within the drill string during withdrawal and disconnection of thedrill string. At disconnecting a drill string section, a pressure airimpulse is introduced into the flushing channel thereof so as to lowerthe liquid level and thereby avoid liquid over-flow at the top of thecasing tube. A back-flow restricting valve prevents rapid rising of theliquid level within the drill string. A preventer unit having a pressurebalanced packing sleeve seals off the upper end of the casing tube; thecontact pressure of said packing sleeve is automatically andcontinuously adapted to the actual casing tube pressure by means of apressure responsive control valve which is arranged to release thepacking sleeve from pressure in response to decreasing casing tubepressure.

12 Claims, 4 Drawing Figures PATENTEDJUN 17 I975 SHEET Fig. 1

PATENTEDJUN 17 I975 3, 9 959 SHEET 2 HllllllllH SHEET PATENTEDJUN 17I975 4 U \\/A/ L PATENTEIJJUHH ms -:BBSBSS SHEET 1 EARTH DRILLINGAPPARATUS This invention relates to a drilling apparatus for pressuredrilling through the earth, and more particularly to a device formaintaining the drill hole pressure during withdrawal and disconnectionof the drill string.

An object of the invention is to provide a preventer unit for sealingoff the casing tube during drilling and vertical travel of the drillstring, the preventer being provided with a long-life packing sleeve.

A further object of the invention is to provide a means for controllingthe contact pressure of the preventer unit packing sleeve with respectto the casing tube pressure.

Further objects and advantages of the invention will be apparent fromthe detailed description and the drawings BRIEF DESCRIPTION OF THEDRAWINGS FIGS. 1 and 2 schematically show a drilling apparatus accordingto the invention, FIG. 1 showing the drilling apparatus in its drillingposition, and FIG. 2 showing the drill string withdrawing position andalso showing a pressure air injection device;

FIG. 3 is a longitudinal section through a preventer unit according tothe invention, the preventer unit being shown in its active, as well asin its non-active position; and

FIG. 4 shows a longitudinal section through a pres sure control valveintended for adapting the contact pressure of the preventer unit incorrespondence to the actual pressure in the casing tube.

DETAILED DESCRIPTION The drilling apparatus shown in FIG. 1 comprisesmainly a drill string 1, a drilling machine 2 for rotating the drillstring 1, a casing tube assembly 3 and a liquid handling system 4.

The drill string 1 is constituted by a number of conventional drill tubesections and is terminated at its forward or lower end by a core tubeprovided with an annular diamond bit. (Not shown). At its rear or upperend, the drill string 1 is provided with a water swivel 5 and adjacentits forward end, the drill string is provided with a backflowrestricting valve 6. The valve 6 has to be located above the core tube.

The backflow restricting valve 6 is in fact a check valve provided witha restricted by-pass opening through which the drill string is slowlytilled up when it is lowered down into a water containing hole. Thebypass opening should be of such a size that the drill string is filledup with water as it has reached the bottom of the hole. Thereby, thedrilling operation can be started immediately.

The drilling machine 2 comprises a housing 7, a motor 8, a rotatingchuck 9, a feeding device 10 for accomplishing longitudinal movements ofthe drilling machine and a stationary chuck 11. The drilling machine 2is intended for positive feeding, retracting and disconnecting the drillstring. Such a drilling machine is shown in Swedish patent No. 324,747,corresponding to US. Pat. No. 3,613,804.

The casing tube assembly 3 comprises a casing tube 12, a gate valve 13located at the upper end of the easing tube and intended for closing thecasing tube when the drill string is withdrawn. The casing tube assemblyalso comprises an emergency preventer 14 of a conventional type forsealing off the casing tube 12 when the drill string 1 is presenttherein but stationary. Finally, the casing tube assembly comprises apreventer unit 15 according to the invention, the object of which is toseal off the casing tube 12 during drilling and withdrawal of the drillstring. The main component of the preventer unit 15 is an annularpressure fluid actuated packing sleeve 17 (see FIG. 3). The preventerunit 15 is herebelow described in detail.

The liquid handling system 4 is intended for providing the drill holewith flushing medium through the drill string 1. The liquid handlingsystem 4 comprises means for restricting the return flow in order toestablish an over-atmospheric pressure in the drill hole. For thatpurpose the liquid handling system 4 is split up into two main branches,namely one feed branch 18 and one re turn branch 19. The feed branch 18comprises a pump P2, a manometer M2 and a flow meter F1 and is connectedto the water swivel 5 through a conduit 21.

The return branch 19 of the liquid handling system 4 is connected to thecasing tube 12 through a conduit and comprises a flow meter F2, amanometer M3 and a variable restricting device S2. Moreover, the returnbranch 19 contains a more sensitive flow meter 22 which is connecteddownstream of the restricting means S2. Flow meter 22 is provided withan outlet conduit 23 containing a variable restricting means S3.Further, the sensitive flow meter 22 includes a vessel having one of itswalls made of a transparent material. Through this wall, the liquidlevel within the vessel is observable from the outside. Rising orsinking of the liquid level indicates variations in the return flow. Thevessel is also provided with an overflow outlet D6 through which drillhole gas is exhausted. Owing to the fact that the return flow branch 19of the liquid handling system is closed up to the flow meter 22, it ispossible to control the gas outlet. Such a gas is very often unhealthy.

The return flow branch 19 also contains a constant pressure valve T2which is arranged in parallel with the flow restricting means S2 andconnected to the threeposition valve V4. During intermittent flow in thesystem the valve T2 is put into action by shifting the valve V4.

The return flow branch 19 of the liquid handling system 4 also containsa variable displacement pump P3 and two additional outlets D3 and D4.The outlet D3 contains a flow restricting means S4 and the outlet D4contains a safety valve T1 the opening pressure of which is adjustableand normally set on the top pressure limit of the casing tube. This partof the system, together with the flow meter F2 and the manometer M3, issuspendable from the rest of the system by means of a valve V3.

The pump P3 is driven by a pressure compensated hydraulic motor (notshown) and is intended to be put into work in order to maintain thedrill hole pressure and thereby avoid collapsing of the drill hole wallif the regularly working pump P2 is stopped or if the liquid loss in thehole rapidly increases. In the latter case, the pump P3 can be suppliedwith a thicker flushing liquid in order to obtain a choking up of thehigh-porous formations.

The feed and return flow branches 18 and 19, respectively, areinterconnected by a conduit comprising a three-position valve V2 and amanometer M4 which is intended for calibration purposes.

Furthermore, the drilling apparatus comprises a pressure fluid systemfor actuating the preventer unit 15. This pressure fluid systemcomprises a pump P1 and is connected to the casing tube 12 via apressure control valve S1.

The pressure control valve S1 comprises a housing 31 and a spring biasedvalve piston 32 (see FIG. 4). The valve piston 32 is biased in onedirection partly by means of a pressure spring 33 and partly by thecasing tube pressure through a pressure sensing conduit 99. The biasingforce of the spring 33 is adjustable by a screw 35. The valve piston 32is also exposed to a counter-directed force constituted by the pressurefrom the pump P1. The pump pressure actuated end of the valve piston 32is of a smaller diameter than the opposite end and is provided with avalve seat portion for cooperation with an annular seat 34 in thehousing. The housing 31 is provided with an outlet D2 which is solocated that, when the piston 32 is pushed away from the seat 34 by thepump pressure, the pump is drained through the outlet D2.

As the pump P1 has a determined flow capacity, the pressure in thesystem which is the pressure acting upon the packing sleeve 17 of thepreventer unit is dependent on the size of the drainage opening. Thedrainage opening is defined by the seat 34 and the valve piston 32.Oppositely, the opening force acting upon the valve piston is dependenton the pressure in the system. The size of the drainage opening is alsodependent on the counter directed force of the spring 33 and the casingtube pressure which act upon the opposite end of the valve piston. Thus,the latter is acted upon by two oppositely directed fluid pressures andgives at a certain setting of the spring force a greater drainageopening when the pressure in the casing tube decreases. The result ofthat is that the pressure in the system as well as the pressure actingupon the packing sleeve 17 decreases. The relationship between thepressure in the casing tube and the pressure in the liquid system can beadjusted by means of the screw 35. The pressure fluid system can bedrained to an outlet D1 by means of a valve V1.

Moreover, the pressure fluid system contains a manometer M1 and aconduit for connection with the return flow branch 19 of the liquidhandling system, which conduit contains a check valve T3.

Referring to FIG. 3, the preventer unit 15 comprises a housing 40 whichis provided with a central opening for the drill string 1. Within thehousing 40 there is rotatably mounted a retainer ring 41 which isconnected to the pressure fluid system through an opening 42 in thehousing 40.

The packing sleeve 17 is rigidly secured in the retainer ring 41 in sucha way that pressure fluid from the pump P1 has access to its outside forapplying a radial contact force and make it engage the drill string withits inside. To the left in FIG. 3, the packing sleeve 17 is shown in itspressure released rest position and to the right in the same figure thepacking sleeve 17 is shown in its active position.

As seen in FIG. 3, the packing sleeve 17 is provided with two axiallyspaced contact portions 45 and 46 which are intended to cooperate withthe drill string when the packing sleeve is pressurized. i

During axial movement of the drill string 1, the packing sleeve 17slides along the drill string. In order to limit the friction forcearising upon the packing sleeve 17, the latter is provided with a numberof small diameter leakage openings 43 which are located intermediate thecontact portions 45 and 46. Through these leakage openings 43, pressurefluid is able to leak out between the packing sleeve 17 and the drillstring 1. Thereby. a pressure balancing of the packing sleeve isaccomplished. By this arrangement not only a limitation of the contactpressure between the packing sleeve and the drill string is obtained butalso a lubrication of the contact surfaces.

As the difference between the actuating pressure of the packing sleeve17 and the drill hole pressure is less than the difference between theactuating pressure and the atmosphere, the sleeve 17 may very well benonsymmetric, which means that it is thicker at its upper end than atits lower end. In order to obtain an equal pressure balancing andlubrication of the packing sleeve 17 throughout its length, the leakageopenings may be placed somewhat closer to that end of the packing sleevewhich is closest to the drill hole. The packing sleeve 17 may very wellbe made of rubber or plastic. As water is used as pressure fluid in thesystem, it is very easy to obtain lubrication of the retainer ring 41 byusing bearing surfaces made of rubber, plastic and the like. By thisarrangement the bearing surfaces of the retainer ring do not have to bepacked in.

FIG. 2 shows the same drill equipment as FIG. 1 but in FIG. 2 it isshown in position withdrawal of the drill string. In this position, thewater swivel 5 is disconnected from the rear end of the drill string anda hydraulically operated air injection device 50 is fitted. The objectof this device is to connect the drill string 1 to a pressure airsource. To obtain a proper connection between the air injection deviceand the drill string, the drilling machine 2 is provided with a couplingsleeve 48 which extends rearwardly from the rotatable chuck 9.

The air injection device 50 comprises a swing arm 49 upon which ismounted a tapered connecting member 51. The connecting member 51 ismovable by means of the swing arm between an active position (as in FIG.2) and a non-active position (as in FIG. 1) and is provided with aconical outer surface 53 for cooperation with the rear end of thecoupling sleeve 48. The swinging arm 49 is actuated by means of ahydraulic cylinder 52 which is connected to a pump 54 via a controlvalve 55.

The pressure air system which communicates with the connecting member 51comprises a compressor 57, a pressure air tank 58 and a control valve59.

The operation order of the above described drilling equipment is thefollowing.

At the start of the drilling operation, the lower part of the drillstring 1 containing the drill bit, the core tube and the backflowrestricting valve 6 is introduced through the drilling machine 2 and thecasing tube assembly 3. Thereafter, the drilling operation is carriedout in a conventional manner in that the chuck 9 rotates the drillstring 1 at the same time as the feeding device 10 forces the drillstring 1 downwards. The feed branch 18 of the liquid handling system 4is connected to the drill string by means of the water swivel 5. Duringdrilling, the safety preventer l4 and the gate valve 13 are fullyopened, while the preventer unit 15 is activated by the pressure fluidsystem pump P1. The drill hole is continuously flushed by a liquiddelivered by the pump P2, the feed pressure being indicated at themanometer M2 and the fluid flow being indicated at the flow meter F1.The flushing liquid is pumped down the hole through the interior of thedrill string 1 and returns to the surface at the outside of the drillstring. As the drill hole is closed by means of the preventer unit 15,the flushing liquid is forced out into the return flow branch 19 of theliquid handling system 4 Because of porosity in the penetratedformations, losses of flushing liquid always occur, which means that thereturn flow is less than the feed flow. The actual return flow isindicated on the flow meter F2.

During drilling, the valve V3 is open, the valve V2 is closed betweenthe feed branch l8 and the return flow branch 19 and the valve V4 isopen toward the flow restricting means S2. The pressure in the returnflow branch 19 is indicated on the manometers M4 and M3.

At the beginning of the drilling operation, the flow restricting meansS2 and S3 is set so as to match an estimated return flow or so as tomatch a certain loss of liquid in the drill hole. The restriction meansS2 gives a desirable return flow pressure. The restriction means S3should be set so that the liquid level within the vessel 22 remainsstationary at a certain level. If a considerable increase or decrease inthe flush liquid losses occurs, it could be observed upon the flow meterF2. On the other hand, if the liquid losses in the drill hole arediminutive, it could be observed upon the flow meter 22. The flow meter22 is very sensitive because of the fact that even a very little changein return flow is indicated as a successive rising or sinking of theliquid level. This high sensitivity makes it possible to discover gasinflow into the drill hole at an early stage which is very importantfrom the safety point of view, because the operators get more time fortaking precautionary measurements in order to avoid blow-outs.

In order to maintain the liquid pressure in the drill hole, when thewater swivel 5 and the feed branch 18 of the liquid handling system isdisconnected from the drill string 1, the valve V2 is closed toward thewater swivel and the valve T2 is activated by shifting the valve V4. Bythis arrangement the liquid pressure in the drill hole is maintained.

Owing to the fact that the hydrostatic pressure within the drill holeincreases as the depth of the drill hole increases, the pressure of theflushing liquid has to be adapted thereto in order to control occurringgas inflow into the drill hole. For making the preventer unit seal offthe drill hole around the drill string at increasing pressure, a highercontact pressure has to be applied upon the packing sleeve 17. Thispressure adaptation is accomplished by the pressure control valve S1which communicates with the casing tube 12 through the pressure sensingconduit 99. As the casing tube pressure increases, the pressure requiredto obtain drainage of the pump Pl also increases. This means that thedrainage of the pump P1 decreases and the pressure in the pressure fluidsystem as well as the contact pressure of the preventer unit packingsleeve 17 increases. The actual pressure in the pressure fluid systemcan be observed on the manometer M1 and could be adapted manually bysetting of the screw 35 of the pressure control valve S1.

At withdrawal and disconnection of the drill string 1, which is carriedout in a common way by cooperation between the chucks 9 and 11 of thedrilling machine and the feeding device 10, the water swivel 5 isdisconnected, whereby the liquid pressure within the drill stringceases. In order to prevent the liquid within the chine above thepreventer unit 15, the connecting member 51 is swung into engagementwith the coupling sleeve 48. Pressure air is introduced into the drillstring in the form of a pressure air impulse. The purpose of thepressure air impulse is to press down the liquid level within the drillstring a certain distance below the uppermost drill string joint. Then,the air injection device is disconnected by shifting of the valve 55 andthe uppermost drill string section is disconnected. As soon as thedisconnected drill string section has been removed, the pressure airsystem is reconnected to the drill string.

The liquid level within the drill string has to be lowered to such a lowlevel that a pressure that may remain in the drill string, is not ableto raise the liquid level up to the section joint that has just beenbroken during the time interval when the air injection device isremoved. The liquid level rising speed depends on the size of theby-pass opening of the backflow restricting valve 6. If the by-passopening through'this valve 6 has a proper size the liquid level does notreach the upper end of the drill string and any liquid overflow does notoccur. At the top of the casing tube assembly 3, there is mounted afunnel 56, the object of which is to collect overflowing liquid in thecase the liquid level rises too fast in the drill string. The funnel isprovided with an outlet D7 through which liquid is drained to the tank.

As previously mentioned, an annular diamond bit is used and a core isformed throughout the hole. For that purpose, a single-walled core tubeis used in order to obtain greatest possible core diameter. This meansthat the drill string has to be withdrawn from the drill hole every timethe core tube has to be emptied. However, the drilling machine of theabove described type, is especially well fitted for that purpose in thathandling of the drill string sections is fully mechanized, andconnection and disconnection of the drill string section is carried outvery fast.

On the other hand, the single-walled core tube makes it possible to usea thin-walled drill bit which requires quite a little power with regardto rotation as well as feeding movements. Furthermore, this method makesit possible to continuously obtain information about the penetratedformations.

With the shown drilling apparatus a light and lowviscous flushing liquidis used, the density of which substantially corresponds to that ofwater. However, the flushing liquid contains some additives for instancefor transportation of drill cuttings and for stabilizing the drilledhole. For the stabilizing purpose, the cuttings produced are used asreinforcement in the drill hole walls. The invention is not limited tothe shown and described embodiment but can be freely varied within thescope of the claims.

What I claim is:

l. Preventer unit for establishing a seal between a casing tube and adrill stem during pressure drilling through the earth, comprising anelastic packing sleeve rotatably mounted on the casing tube, the outsideof said packing sleeve communicating with a pressure fluid source forapplying a contact pressure upon the drill string, said preventer unitfurther comprising a pressure control valve which is connected to saidfluid pressure source as well as to the casing tube pressure and whichis arranged to automatically adapt the packing sleeve contact pressurein response to the casing tube pressure by controlling a pressure fluidsource drainage.

2. Preventer unit according to claim 1, wherein the pressure controlvalve comprises a housing containing a slidable valve piston, a valveseat and a drain outlet, said valve piston being provided with a valveseat matching surface at its one end which communicates with saidpressure fluid source, while its other end communicates with the casingtube pressure, said drain outlet being connected to said pressure fluidsource via the valve seat. I

3. Preventer unit according to claim 2 wherein the packing sleeve isprovided with at least one leakage opening through which pressure fluidhas access to the inner surface of the packing sleeve.

4. Preventer unit according to claim 1,wherein the packing sleeve isprovided with at least one leakage opening through which pressure fluidhas access to the inner surface of the packing sleeve.

5. Preventer unit according to claim 4, wherein the packing sleeve hastwo axially spaced contact portions between which said leakage openingis located.

6. Preventer unit according to claim 4 wherein said at least one leakageopening extends from a radially outer surface of the packing sleeve tothe inner surface of the packing sleeve. i

7. Preventer unit according to claim 4 wherein said packing sleeve isthicker at its upper end than at its lower end and wherein said at leastone leakage opening is located closer to the lower end of said packingsleeve than to the upper end thereof.

8. Preventer unit according to claim 1 wherein said packing sleeve isthicker at its upper end than at its lower end.

9. Preventer unit according to claim 1 wherein said pressure controlvalve controls said pressure fluid source drainage so as to cause thepacking sleeve contact pressure to increase in response to increasingcasing tube pressure.

10. Preventer unit according to claim 9 wherein said pressure controlvalve decreases the pressure fluid source drainage in response toincreasing casing tube pressure.

11. Preventer unit according to claim 1 wherein said pressure controlvalve controls said pressure fluid source drainage so as to cause thepacking sleeve contact pressure to decrease in response to decreasingcasing tube pressure.

12. Preventer unit according to claim 11 wherein said pressure controlvalve increases the pressure fluid source drainage-in response todecreasing casing tube pressure.

1. Preventer unit for establishing a seal between a casing tube and adrill stem during pressure drilling through the earth, comprising anelastic packing sleeve rotatably mounted on the casing tube, the outsideof said packing sleeve communicating with a pressure fluid source forapplying a contact pressure upon the drill string, said preventer unitfurther comprising a pressure control valve which is connected to saidfluid pressure source as well as to the casing tube pressure and whichis arranged to automatically adapt the packing sleeve contact pressurein response to the casing tube pressure by controlling a pressure fluidsource drainage.
 2. Preventer unit according to claim 1, wherein thepressure control valve comprises a housing containing a slidable valvepiston, a valve seat and a drain outlet, said valve piston beingprovided with a valve seat matching surface at its one end whichcommunicates with said pressure fluid source, while its other endcommunicates with the casing tube pressure, said drain outlet beingconnected to said pressure fluid source via the valve seat.
 3. Preventerunit according to claim 2 wherein the packing sleeve is provided with atleast one leakage opening through which pressure fluid has access to theinner surface of the packing sleeve.
 4. Preventer unit according toclaim 1, wherein the packing sleeve is provided with at least oneleakage opening through which pressure fluid has access to the innersurface of the packing sleeve.
 5. Preventer unit according to claim 4,wherein the packing sleeve has two axially spaced contact portionsbetween which said leakage opening is located.
 6. Preventer unitaccording to claim 4 wherein said at least one leakage opening extendsfrom a radially outer surface of the packing sleeve to the inner surfaceof the packing sleeve.
 7. Preventer unit according to claim 4 whereinsaid packing sleeve is thicker at its upper end than at its lower endand wherein said at least one leakage opening is located closer to thelower end of said packing sleeve than to the upper end thereoF. 8.Preventer unit according to claim 1 wherein said packing sleeve isthicker at its upper end than at its lower end.
 9. Preventer unitaccording to claim 1 wherein said pressure control valve controls saidpressure fluid source drainage so as to cause the packing sleeve contactpressure to increase in response to increasing casing tube pressure. 10.Preventer unit according to claim 9 wherein said pressure control valvedecreases the pressure fluid source drainage in response to increasingcasing tube pressure.
 11. Preventer unit according to claim 1 whereinsaid pressure control valve controls said pressure fluid source drainageso as to cause the packing sleeve contact pressure to decrease inresponse to decreasing casing tube pressure.
 12. Preventer unitaccording to claim 11 wherein said pressure control valve increases thepressure fluid source drainage in response to decreasing casing tubepressure.